Merge rust-bitcoin/rust-secp256k1#353: Documented features

18f74d5242 Clarify what does "less security" mean (Martin Habovstiak)
94c55b4d09 Fixed typos/grammar mistakes (Martin Habovštiak)
1bf05523f0 Documented features (Martin Habovstiak)

Pull request description:

  This documents the Cargo features making sure docs.rs shows warning for
  feature-gated items. They are also explicitly spelled out in the crate
  documentation.

  The PR is similar in spirit to https://github.com/rust-bitcoin/rust-bitcoin/pull/633

ACKs for top commit:
  apoelstra:
    ACK 18f74d5242

Tree-SHA512: 8aac3fc5fd8ee887d6b13606d66b3d11ce44662afb92228c4f8da6169e3f70ac6a005b328f427a91d307f8d36d091dcf24bfe4d17dfc034d02b578258719a90a

Cargo.toml

@@ -15,6 +15,7 @@ autoexamples = false # Remove when edition 2018 https://github.com/rust-lang/car
 # Should make docs.rs show all functions, even those behind non-default features
 [package.metadata.docs.rs]
 features = [ "rand", "rand-std", "serde", "recovery" ]
+rustdoc-args = ["--cfg", "docsrs"]
 
 [features]
 unstable = ["recovery", "rand-std"]

secp256k1-sys/Cargo.toml

@@ -17,6 +17,7 @@ links = "rustsecp256k1_v0_4_1"
 # Should make docs.rs show all functions, even those behind non-default features
 [package.metadata.docs.rs]
 features = [ "recovery", "lowmemory" ]
+rustdoc-args = ["--cfg", "docsrs"]
 
 [build-dependencies]
 cc = "1.0.28"

secp256k1-sys/src/lib.rs

@@ -23,6 +23,8 @@
 #![deny(unused_mut)]
 
 #![cfg_attr(all(not(test), not(feature = "std")), no_std)]
+#![cfg_attr(docsrs, feature(doc_cfg))]
+
 #[cfg(any(test, feature = "std"))]
 extern crate core;
 
@@ -34,6 +36,7 @@ mod macros;
 pub mod types;
 
 #[cfg(feature = "recovery")]
+#[cfg_attr(docsrs, doc(cfg(feature = "recovery")))]
 pub mod recovery;
 
 use core::{slice, ptr};
@@ -524,6 +527,7 @@ extern "C" {
 //  In:      flags: which parts of the context to initialize.
 #[no_mangle]
 #[cfg(all(feature = "std", not(rust_secp_no_symbol_renaming)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "std", not(rust_secp_no_symbol_renaming)))))]
 pub unsafe extern "C" fn rustsecp256k1_v0_4_1_context_create(flags: c_uint) -> *mut Context {
     use core::mem;
     use std::alloc;
@@ -543,6 +547,7 @@ pub unsafe extern "C" fn rustsecp256k1_v0_4_1_context_create(flags: c_uint) -> *
 }
 
 #[cfg(all(feature = "std", not(rust_secp_no_symbol_renaming)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "std", not(rust_secp_no_symbol_renaming)))))]
 pub unsafe fn secp256k1_context_create(flags: c_uint) -> *mut Context {
     rustsecp256k1_v0_4_1_context_create(flags)
 }
@@ -555,6 +560,7 @@ pub unsafe fn secp256k1_context_create(flags: c_uint) -> *mut Context {
 ///
 #[no_mangle]
 #[cfg(all(feature = "std", not(rust_secp_no_symbol_renaming)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "std", not(rust_secp_no_symbol_renaming)))))]
 pub unsafe extern "C" fn rustsecp256k1_v0_4_1_context_destroy(ctx: *mut Context) {
     use std::alloc;
     secp256k1_context_preallocated_destroy(ctx);
@@ -565,6 +571,7 @@ pub unsafe extern "C" fn rustsecp256k1_v0_4_1_context_destroy(ctx: *mut Context)
 }
 
 #[cfg(all(feature = "std", not(rust_secp_no_symbol_renaming)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "std", not(rust_secp_no_symbol_renaming)))))]
 pub unsafe fn secp256k1_context_destroy(ctx: *mut Context) {
     rustsecp256k1_v0_4_1_context_destroy(ctx)
 }

src/context.rs

@@ -6,9 +6,11 @@ use Error;
 use Secp256k1;
 
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(docsrs, doc(cfg(any(feature = "std", feature = "alloc"))))]
 pub use self::alloc_only::*;
 
 #[cfg(feature = "global-context-less-secure")]
+#[cfg_attr(docsrs, doc(cfg(feature = "global-context-less-secure")))]
 /// Module implementing a singleton pattern for a global `Secp256k1` context
 pub mod global {
     #[cfg(feature = "global-context")]
@@ -94,6 +96,7 @@ mod private {
 }
 
 #[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(docsrs, doc(cfg(any(feature = "std", feature = "alloc"))))]
 mod alloc_only {
     #[cfg(feature = "std")]
     use std::alloc;
@@ -108,12 +111,15 @@ mod alloc_only {
     const ALIGN_TO: usize = ::core::mem::align_of::<AlignedType>();
 
     /// Represents the set of capabilities needed for signing.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "std", feature = "alloc"))))]
     pub enum SignOnly {}
 
     /// Represents the set of capabilities needed for verification.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "std", feature = "alloc"))))]
     pub enum VerifyOnly {}
 
     /// Represents the set of all capabilities.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "std", feature = "alloc"))))]
     pub enum All {}
 
     impl Signing for SignOnly {}

src/ecdsa/mod.rs

@@ -9,6 +9,7 @@ use ffi::CPtr;
 mod recovery;
 
 #[cfg(feature = "recovery")]
+#[cfg_attr(docsrs, doc(cfg(feature = "recovery")))]
 pub use self::recovery::{RecoveryId, RecoverableSignature};
 
 /// An ECDSA signature
@@ -279,6 +280,7 @@ impl From<ffi::Signature> for Signature {
 }
 
 #[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
 impl ::serde::Serialize for Signature {
     fn serialize<S: ::serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
         if s.is_human_readable() {
@@ -290,6 +292,7 @@ impl ::serde::Serialize for Signature {
 }
 
 #[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
 impl<'de> ::serde::Deserialize<'de> for Signature {
     fn deserialize<D: ::serde::Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
         if d.is_human_readable() {

src/key.rs

@@ -95,9 +95,10 @@ fn random_32_bytes<R: Rng + ?Sized>(rng: &mut R) -> [u8; 32] {
 }
 
 impl SecretKey {
-    /// Creates a new random secret key. Requires compilation with the "rand" feature.
+    /// Generates a new random secret key.
     #[inline]
     #[cfg(any(test, feature = "rand"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
     pub fn new<R: Rng + ?Sized>(rng: &mut R) -> SecretKey {
         let mut data = random_32_bytes(rng);
         unsafe {
@@ -221,6 +222,7 @@ impl SecretKey {
 }
 
 #[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
 impl ::serde::Serialize for SecretKey {
     fn serialize<S: ::serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
         if s.is_human_readable() {
@@ -233,6 +235,7 @@ impl ::serde::Serialize for SecretKey {
 }
 
 #[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
 impl<'de> ::serde::Deserialize<'de> for SecretKey {
     fn deserialize<D: ::serde::Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
         if d.is_human_readable() {
@@ -467,6 +470,7 @@ impl From<ffi::PublicKey> for PublicKey {
 }
 
 #[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
 impl ::serde::Serialize for PublicKey {
     fn serialize<S: ::serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
         if s.is_human_readable() {
@@ -478,6 +482,7 @@ impl ::serde::Serialize for PublicKey {
 }
 
 #[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
 impl<'de> ::serde::Deserialize<'de> for PublicKey {
     fn deserialize<D: ::serde::Deserializer<'de>>(d: D) -> Result<PublicKey, D::Error> {
         if d.is_human_readable() {
@@ -586,9 +591,10 @@ impl KeyPair {
         }
     }
 
-    /// Creates a new random secret key. Requires compilation with the "rand" feature.
+    /// Generates a new random secret key.
     #[inline]
     #[cfg(any(test, feature = "rand"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
     pub fn new<R: ::rand::Rng + ?Sized, C: Signing>(secp: &Secp256k1<C>, rng: &mut R) -> KeyPair {
         let mut random_32_bytes = || {
             let mut ret = [0u8; 32];
@@ -685,6 +691,7 @@ impl str::FromStr for KeyPair {
 }
 
 #[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
 impl ::serde::Serialize for KeyPair {
     fn serialize<S: ::serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
         if s.is_human_readable() {
@@ -698,6 +705,7 @@ impl ::serde::Serialize for KeyPair {
 }
 
 #[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
 impl<'de> ::serde::Deserialize<'de> for KeyPair {
     fn deserialize<D: ::serde::Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
         if d.is_human_readable() {
@@ -954,6 +962,7 @@ impl From<::key::PublicKey> for XOnlyPublicKey {
 }
 
 #[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
 impl ::serde::Serialize for XOnlyPublicKey {
     fn serialize<S: ::serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
         if s.is_human_readable() {
@@ -965,6 +974,7 @@ impl ::serde::Serialize for XOnlyPublicKey {
 }
 
 #[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
 impl<'de> ::serde::Deserialize<'de> for XOnlyPublicKey {
     fn deserialize<D: ::serde::Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
         if d.is_human_readable() {

src/lib.rs

@@ -110,6 +110,21 @@
 //! Observe that the same code using, say [`signing_only`](struct.Secp256k1.html#method.signing_only)
 //! to generate a context would simply not compile.
 //!
+//! ## Crate features/optional dependencies
+//!
+//! This crate provides the following opt-in Cargo features:
+//!
+//! * `std` - use standard Rust library, enabled by default.
+//! * `alloc` - use the `alloc` standard Rust library to provide heap allocations.
+//! * `rand` - use `rand` library to provide random generator (e.g. to generate keys).
+//! * `rand-std` - use `rand` library with its `std` feature enabled. (Implies `rand`.)
+//! * `recovery` - enable functions that can compute the public key from signature.
+//! * `lowmemory` - optimize the library for low-memory environments.
+//! * `global-context` - enable use of global secp256k1 context. (Implies `std`, `rand-std` and
+//!                      `global-context-less-secure`.)
+//! * `global-context-less-secure` - enables global context without extra sidechannel protection.
+//! * `serde` - implements serialization and deserialization for types in this crate using `serde`.
+//! * `bitcoin_hashes` - enables interaction with the `bitcoin-hashes` crate (e.g. conversions).
 
 // Coding conventions
 #![deny(non_upper_case_globals)]
@@ -121,21 +136,35 @@
 
 #![cfg_attr(all(not(test), not(feature = "std")), no_std)]
 #![cfg_attr(all(test, feature = "unstable"), feature(test))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
 #[macro_use]
 pub extern crate secp256k1_sys;
 pub use secp256k1_sys as ffi;
 
-#[cfg(feature = "bitcoin_hashes")] pub extern crate bitcoin_hashes as hashes;
+#[cfg(feature = "bitcoin_hashes")]
-#[cfg(all(test, feature = "unstable"))] extern crate test;
+#[cfg_attr(docsrs, doc(cfg(feature = "bitcoin_hashes")))]
-#[cfg(any(test, feature = "rand"))] pub extern crate rand;
+pub extern crate bitcoin_hashes as hashes;
-#[cfg(any(test))] extern crate rand_core;
+#[cfg(all(test, feature = "unstable"))]
-#[cfg(feature = "serde")] pub extern crate serde;
+extern crate test;
-#[cfg(all(test, feature = "serde"))] extern crate serde_test;
+#[cfg(any(test, feature = "rand"))]
-#[cfg(any(test, feature = "rand"))] use rand::Rng;
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
-#[cfg(any(test, feature = "std"))] extern crate core;
+pub extern crate rand;
-#[cfg(all(test, target_arch = "wasm32"))] extern crate wasm_bindgen_test;
+#[cfg(any(test))]
-#[cfg(feature = "alloc")] extern crate alloc;
+extern crate rand_core;
+#[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
+pub extern crate serde;
+#[cfg(all(test, feature = "serde"))]
+extern crate serde_test;
+#[cfg(any(test, feature = "rand"))]
+use rand::Rng;
+#[cfg(any(test, feature = "std"))]
+extern crate core;
+#[cfg(all(test, target_arch = "wasm32"))]
+extern crate wasm_bindgen_test;
+#[cfg(feature = "alloc")]
+extern crate alloc;
 
 
 #[macro_use]
@@ -163,6 +192,7 @@ use core::{mem, fmt, str};
 use ffi::{CPtr, types::AlignedType};
 
 #[cfg(feature = "global-context-less-secure")]
+#[cfg_attr(docsrs, doc(cfg(feature = "global-context-less-secure")))]
 pub use context::global::SECP256K1;
 
 #[cfg(feature = "bitcoin_hashes")]
@@ -196,6 +226,7 @@ pub trait ThirtyTwoByteHash {
 }
 
 #[cfg(feature = "bitcoin_hashes")]
+#[cfg_attr(docsrs, doc(cfg(feature = "bitcoin_hashes")))]
 impl ThirtyTwoByteHash for hashes::sha256::Hash {
     fn into_32(self) -> [u8; 32] {
         self.into_inner()
@@ -203,6 +234,7 @@ impl ThirtyTwoByteHash for hashes::sha256::Hash {
 }
 
 #[cfg(feature = "bitcoin_hashes")]
+#[cfg_attr(docsrs, doc(cfg(feature = "bitcoin_hashes")))]
 impl ThirtyTwoByteHash for hashes::sha256d::Hash {
     fn into_32(self) -> [u8; 32] {
         self.into_inner()
@@ -210,6 +242,7 @@ impl ThirtyTwoByteHash for hashes::sha256d::Hash {
 }
 
 #[cfg(feature = "bitcoin_hashes")]
+#[cfg_attr(docsrs, doc(cfg(feature = "bitcoin_hashes")))]
 impl<T: hashes::sha256t::Tag> ThirtyTwoByteHash for hashes::sha256t::Hash<T> {
     fn into_32(self) -> [u8; 32] {
         self.into_inner()
@@ -256,6 +289,7 @@ impl Message {
     /// assert_eq!(m1, m2);
     /// ```
     #[cfg(feature = "bitcoin_hashes")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "bitcoin_hashes")))]
     pub fn from_hashed_data<H: ThirtyTwoByteHash + hashes::Hash>(data: &[u8]) -> Self {
         <H as hashes::Hash>::hash(data).into()
     }
@@ -316,6 +350,7 @@ impl fmt::Display for Error {
 }
 
 #[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 impl std::error::Error for Error {}
 
 
@@ -374,6 +409,7 @@ impl<C: Context> Secp256k1<C> {
     /// see comment in libsecp256k1 commit d2275795f by Gregory Maxwell. Requires
     /// compilation with "rand" feature.
     #[cfg(any(test, feature = "rand"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
     pub fn randomize<R: Rng + ?Sized>(&mut self, rng: &mut R) {
         let mut seed = [0u8; 32];
         rng.fill_bytes(&mut seed);
@@ -406,6 +442,7 @@ impl<C: Signing> Secp256k1<C> {
     /// with the "rand" feature.
     #[inline]
     #[cfg(any(test, feature = "rand"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
     pub fn generate_keypair<R: Rng + ?Sized>(&self, rng: &mut R)
                                     -> (key::SecretKey, key::PublicKey) {
         let sk = key::SecretKey::new(rng);

src/schnorr.rs

@@ -19,6 +19,7 @@ impl_array_newtype!(Signature, u8, constants::SCHNORRSIG_SIGNATURE_SIZE);
 impl_pretty_debug!(Signature);
 
 #[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
 impl ::serde::Serialize for Signature {
     fn serialize<S: ::serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
         if s.is_human_readable() {
@@ -30,6 +31,7 @@ impl ::serde::Serialize for Signature {
 }
 
 #[cfg(feature = "serde")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serde")))]
 impl<'de> ::serde::Deserialize<'de> for Signature {
     fn deserialize<D: ::serde::Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
         if d.is_human_readable() {
@@ -117,6 +119,7 @@ impl<C: Signing> Secp256k1<C> {
     /// generator to generate the auxiliary random data.
     /// Requires compilation with "rand-std" feature.
     #[cfg(any(test, feature = "rand-std"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rand-std")))]
     #[deprecated(since = "0.21.0", note = "Use sign_schnorr instead.")]
     pub fn schnorrsig_sign(&self, msg: &Message, keypair: &KeyPair) -> Signature {
         self.sign_schnorr(msg, keypair)
@@ -126,6 +129,7 @@ impl<C: Signing> Secp256k1<C> {
     /// generator to generate the auxiliary random data.
     /// Requires compilation with "rand-std" feature.
     #[cfg(any(test, feature = "rand-std"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rand-std")))]
     pub fn sign_schnorr(&self, msg: &Message, keypair: &KeyPair) -> Signature {
         let mut rng = thread_rng();
         self.sign_schnorr_with_rng(msg, keypair, &mut rng)
@@ -179,6 +183,7 @@ impl<C: Signing> Secp256k1<C> {
     /// generate the auxiliary random data. Requires compilation with "rand"
     /// feature.
     #[cfg(any(test, feature = "rand"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
     #[deprecated(since = "0.21.0", note = "Use sign_schnorr_with_rng instead.")]
     pub fn schnorrsig_sign_with_rng<R: Rng + CryptoRng>(
         &self,
@@ -193,6 +198,7 @@ impl<C: Signing> Secp256k1<C> {
     /// generate the auxiliary random data. Requires compilation with "rand"
     /// feature.
     #[cfg(any(test, feature = "rand"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
     pub fn sign_schnorr_with_rng<R: Rng + CryptoRng>(
         &self,
         msg: &Message,
@@ -250,6 +256,7 @@ impl <C: Signing> Secp256k1<C> {
     /// with the "rand" feature.
     #[inline]
     #[cfg(any(test, feature = "rand"))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
     pub fn generate_schnorrsig_keypair<R: Rng + ?Sized>(
         &self,
         rng: &mut R,

src/secret.rs

@@ -22,6 +22,7 @@ macro_rules! impl_display_secret {
     // Default hasher exists only in standard library and not alloc
     ($thing:ident) => {
         #[cfg(feature = "std")]
+        #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
         impl ::core::fmt::Debug for $thing {
             fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                 use ::core::hash::Hasher;